1. Field of The Invention
This invention relates to water storage vessels used for potable water supplies. More particularly, it refers to such vessels used as water heaters with direct-fired combustion chambers.
In known water heaters and storage vessels such as described in U.S. Pat. No. 3,207,358, the vessel itself, typically a steel tank, is coated with a corrosion resistant material. This material, designed to protect the tank from the corrosive effects of water is generally applied directly to the tank surface. This may be done through the application of a spray-on plastic type material, electrochemically plating the material, a slush type molding process or more recently, electroless nickel coatings. In each of these processes, the coating material is integrally bonded to the vessel interior. While these coatings do provide a reasonable degree of protection to the vessel interior, their drawbacks are numerous.
In most cases, preparation of the tank itself is critical for proper adhesion of the coating. This generally requires sandblasting or chemical etching of the vessel to be coated. This in itself can be a costly and time consuming process and if not done correctly can result in lining breakdown and tank failure. The majority of lining materials are expensive and vessels often require multiple coats to insure proper coverage, another costly and time consuming process. In those instances where proper coverage is not obtained, the tiniest pinhole or air bubble can result in tank failure.
Because lining failures are internal, when they do occur, the vessel wall is already damaged prior to any external evidence of a problem. Typically, it is not until the water in the vessel causes the exposed metal surface to rust and an external leak develops that the damage is discovered. Repair of this type of failure, if possible at all, is generally expensive and time consuming and often satisfactory results can not be achieved.
Even granting that proper coverage is obtained all lining materials and particularly those in higher temperature applications (160 degrees F) breakdown over time. This makes very desirable the development of an easily replaceable liner. One attempt to do this is found in Adams et al. U.S. Pat. No. 4,981,112. In this design a flexible, non-molded liner is installed within the vessel interior. This design also provides a replaceable liner which facilitates proper operation so that it is not necessary to discard the vessel body in the case of a damaged or defective liner. Several disadvantages of this design are as follows:
(1) The liner is formed by joining one or more seams or weld lines causing the possibility of a flaw in the seam or weld line. In addition, the fabrication of a multiple piece liner requires considerable time and labor. PA1 (2) The lip portion of the liner must be fused or vulcanized to the remainder of the liner. This process is susceptible to the same criticism as in (1) above and again, requires additional labor. PA1 (3) Specially constructed flanges which seal the lining against the tank are required for all openings into the vessel, i.e., hot water outlets, cold water inlet, thermostats, etc. To accommodate these flanges, the tank must be fitted with bolts which are stud welded to the tank. PA1 (4) In some instances, it may be necessary to pull a slight vacuum between the liner and the open interior of the vessel during the liner installation which would increase manufacturing and replacement time and cost.
An improved liner is needed for direct-fired heat exchangers and hot water storage systems.